1. Field of the Invention
The present invention generally relates to the art of microelectronics, and more specifically to the fabrication of a multilayer electrical circuit structure including a plurality of laminated layers of thermally fusible tape, and partially embedded pins extending from the structure for external connection.
2. Description of the Related Art
Multilayer substrates for hybrid microcircuits may be advantageously fabricated using a low temperature cofired ceramic process such as described in an article entitled "DEVELOPMENT OF A LOW TEMPERATURE COFIRED MULTILAYER CERAMIC TECHNOLOGY", by William Vitriol et al. ISHM Proceedings 1983, pp. 593-598. This technology utilizes thermally fusible dielectric sheets in the form of Low-Temperature-Cofired-Ceramic (LTCC) tape.
The LTCC tape sheets may be metallized to make a ground plane, signal plane, bonding plane, or the like, or formed with via holes and back filled with metallization to form interconnect layers. Individual sheets of tape are then stacked on each other, laminated together using a predetermined temperature and pressure, and then fired at a desired elevated temperature at which the material fuses or sinters.
A preferred LTCC, which is known in the art as "green tape", is commercially available from the DuPont Company under the product designation #851AT. The tape contains a material formulation which can be a mixture of glass and ceramic fillers which sinter at about 850.degree. C., and exhibits thermal expansion similar to alumina. The low-temperature processing permits the use of air fired resistors and precious metal thick film conductors such as gold, silver, or their alloys.
Multilayer electrical circuit structures made from LTCC are conventionally mounted in packages, and interconnected with other components and modules in the packages by wire bonds. The wire bonding process is disadvantageous in that it is time consuming, labor intensive, has a high defect rate and does not offer latitude in impedance matching the LTCC elements to the other components.